It’s a steel R.Bike (Reynolds 653 think)- it weighs virtually nothing so I’m guessing the tubes are very thin!

Is the rust going to be a structural problem? or can I wire wool it and patch up the paint?

My commuter is 531

My winter SS is 853

Neither has been washed or rust prrofed and the comuter lives outdoors. I’d just wirewool it and paint over it. Rust is much less dense than steel so a lot of rust can be the result of the loss of not much steel.

grass could do with cutting too.

That’ll probably be okay, you’ll need to gently clean it with wire wool or wet and dry.
I’ve got a 1958 road bike that’s covered in rust and can still do a 100km just fine. On the other hand my 1975 steel crosser folded in two some years back, mind you that was age and tough terrain getting the better of it.